The present invention relates to fluid pumps for elevating fluids from areas such as subterranean hydrocarbon bearing formations. More particularly, the present invention relates to a traveling valve for use on sucker rod pumps.
Conventional oil and gas wells include a cased well bore with a tubing string extending down to the hydrocarbon bearing formation. The casing is perforated at the production level to permit the hydrocarbons to flow into the casing and the bottom of the tubing is generally open to permit the hydrocarbons to flow into the tubing and up to the surface. Oftentimes there is insufficient pressure in a formation to cause oil and other liquids to readily float to the surface. It therefore becomes necessary to install some type of artificial lift system for pumping fluids to the surface.
One of the most common types of artificial lift systems is a sucker rod pump. This type of pump is positioned in the well at the level of the fluids to be removed and is mechanically driven by a series of rods connecting the pump to a pumping unit at the surface.
A sucker rod pump includes the simple combination of a cylinder or barrel with a piston or plunger and a suitable intake valve and a discharge valve. The intake value is often referred to as a standing valve and the discharge valve is often referred to as a traveling valve.
Two of the more common types of sucker rod pumps are the tubing pump in which the pump barrel is attached directly to the tubing and is lowered to the bottom of the well as the tubing is run into the well. The plunger is attached to the bottom of the sucker rod and is positioned within the pump barrel. The intake valve is positioned at the bottom of the pump barrel and the traveling valve is positioned on the plunger. The second type of pump is often referred to as an insert or rod pump and the entire assembly is attached to the bottom of the sucker rod. The barrel is held in place by a special seating nipple or other device positioned within the tubing. This type of pump has the advantage that it can more easily be removed for repair or replacement than a tubing pump. However, it suffers from the disadvantage of having a lower fluid capacity.
The operation of a sucker rod pump is relatively simple. The plunger reciprocates up and down in the barrel under the force of the sucker rod. During the upstroke, the traveling valve is closed and the fluid above the plunger is lifted to the surface by the plunger and sucker rod. At the same time, the standing valve is open allowing fluids to flow into and fill the now evacuated barrel. On the downstroke, the standing valve is closed thus trapping the fluids in the barrel. The traveling valve is opened allowing the compressed fluids to flow through the plunger so they can be lifted during the subsequent cycle.
While sucker rod pumps have been in use for decades and have proven to be economical and reliable, they still experience certain shortcomings and problems. Some of these problems are associated with valves which are generally of the ball and seat variety. This type of valve is opened and closed by pressure differentials across the valve.
One problem that is often encountered is referred to as gas lock. This occurs when there is a substantial amount of gas that flows into the pump with the liquid. Because of the high compressibility of the gas, insufficient pressure is generated during the downstroke of the pump to open the traveling valve against the hydrostatic pressure of the fluid in the production tubing. Accordingly, the pump can repeatedly cycle without any fluid being lifted to the surface.
Fluid pound is another problem that is often encountered. If the barrel is only partially filled with liquid the plunger forcefully encounters the liquid level part way through the downstroke thus causing severe stress to be placed on the pump. Pump off damage also occurs when the barrel is not completely filled with fluid. Damage occurs in the walls of the working barrel due to overheating of the pump which is caused by the absence of fluid to carry away the heat created by friction in the pump.
Accordingly, it would be a significant advancement in the art to provide a traveling valve for a sucker rod pump which could eliminate the problems of gas lock, fluid pound and pump off damage. Such a traveling valve is disclosed and claimed herein.